1. Field of the Invention
The present invention generally relates to image drawing apparatuses for conducting a data transfer by a bit unit with respect to image data being stored in an arbitrary rectangle region in a memory device, and more particularly to an image drawing apparatus that can transfer an image including both a portion where a transmission coefficient is constant and a portion where the transmission coefficient is not constant by one data transfer.
2. Description of the Related Art
Japanese Laid-open Patent Applications No. 7-74927 and No. 9-212410 disclose image drawing apparatuses in that when a data transfer function (hereinafter, called a BITBLT transfer) by a bit unit is conducted with respect to image data stored in an arbitrary block region (or rectangle region) of a memory device, transmission coefficient data (or pixel value) are set in a register when the transmission coefficient data (pixel value) are constant, the transmission coefficient data are read out, and then a transmission drawing process is conducted based on the transmission coefficient data.
Japanese Laid-open Application No. 2003-157433 discloses an image drawing apparatus in that all transmission coefficient data (all pixel values) for the image data are stored in the memory device when the transmission coefficient data (pixel value) are different for each pixel, and the transmission coefficient data are read out for each pixel.
Alternatively, when the transmission coefficient data (pixel value) are given as a function between pixels, a value (memory reference value) stored in the memory device or a value given by a function in a register is read out.
In the above-described conventional image drawing apparatuses, only one of the above three functions is available for a single BITBLT transfer. Accordingly, in a case of a typical icon image as shown in FIG. 1A, even if the transmission coefficient is constant on a periphery of an arrow image, it is required to store transmission coefficients for all pixels in the memory device, and read out a respective transmission coefficient for each pixel. In this case, a larger amount of area blocks of the memory device is unnecessarily used.
On the other hand, as shown in FIG. 1B, it is considered that the icon image is divided into portions where the transmission coefficient is constant and a portion where the transmission coefficient is not constant. In this case, it is required to divide into five rectangle regions and conduct the BITBLT transfer five times. Accordingly, a data amount to transfer becomes larger.
That is, when the BITBLT transfer is conducted with respect to an image including both a portion where the transmission coefficient is constant and a portion where the transmission coefficient is not constant in the image, it is required to store the transmission coefficients for all pixels in the memory device or to divide the rectangle area of the image into a plurality of rectangle regions and conduct the BITBLT transfer for each divided rectangle regions. Accordingly, a larger area used to store the transmission coefficients in the memory device is needed and a larger amount of data to is transferred. In addition, a plurality of the BITBLT transfers makes it complicated.